The effects of different dosages of sodium hexametaphosphate and sodium orthophosphate on corrosion inhibition and water quality in two model water distribution systems, and the corrosion inhibition mechanism on pipe walls were investigated. Results show that adding sodium hexametaphosphate and sodium orthophosphate can not only provide a remedy for the damaged cement coating surface, but improve water quality by reducing hardness, turbidity and total iron in cement-coated water distribution systems. The surface exposed to sodium hexametaphosphate was covered by a discontinuous glass-like film, while the other was covered by some phosphate crystals and a thin film. The glass-like film sequestered Ca, Fe and Al on its surface, where calcium hexametaphosphate could be in complex with Fe2O3 or Al2O3 to form the film, while orthophosphate crystals and the thin film were related to Fe and Ca, FePO4 and Ca3(PO4)2 formed and deposited on the surface composing the thin film.

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